1. Field of the Invention
This invention relates to an ink jet recording apparatus for use in printers, copying machines, facsimile machines, etc., and more particularly to a method for surface-treating an ink jet recording head provided with at least one discharge opening for discharging a recording liquid, particularly in the neighborhood of the discharge opening.
2. Related Background Art
Among various recording systems so far used, the ink jet recording is known as a non-impact recording system with much less generation of noises during the recording, and is also widely admitted to be a very useful recording system, because high speed recording can be carried out on ordinary plain Rapers as a recording medium without any special fixation treatment. Various modes have been also proposed for the ink jet recording system and many improved ink jet recording systems are commercially available. Still now, efforts have been continuously made for the improvements.
FIGS. 1A, 1B, 1C, 1D and 1E show two modes of an ink jet recording head. FIGS. 1A and 1B show ink jet recording heads, each comprising a nozzle with a single discharge opening using a piezo device as an electromechanical converting means, and FIGS. 1C, 1D and 1E show an example of an ink jet recording head comprising a plurality of discharge openings, where an electro-thermo conversion device is provided in each of liquid paths as a means for generating an energy for use in the liquid discharge.
In FIGS. 1A and 1B, numeral 1 is an ink jet recording head, where a body 3 having a fine hollow liquid path 2 is made of, for example, glass, ceramics or metals, and a discharge opening 5 is provided at the tip end of the body 3 to discharge an ink 4 as a recording liquid from the liquid path 2. Numeral 6 is a piezo device provided around the body 3 as a means for generating an energy for use in the liquid discharge, 7 is a tube of, for example, polyethylene, which is connected to the body 3 to supply the ink 4 to the liquid path 2 in the body 3 from an ink tank (not shown in the drawings). The ink 4 can be discharged from the discharge opening 5 by vibration caused by the piezo device 6 to form at least one droplet.
In FIGS. 1C, 1D and 1E, numeral 10 is a support made of glass or ceramics, 11 is an electro-thermal conversion device provided on the substrate 10 as a means for generating an energy for use in the liquid discharge, 12 is a partition wall portion made of a cured film of a photosensitive resin, in which liquid paths 13 that constitute the partition wall portion 12 and discharge openings 14 at the tip end and a liquid chamber 15 are formed by photolithography. Numeral 16 is a second support made of glass, ceramics or metals, and is laminated upon the partition wall portion 12 made of the cured film of a photosensitive resin, for example, by an adhesive 17. Numeral 18 is a supply hole for supplying an ink 4. The latter ink jet recording head 20 is more distinguished in the provision of discharge openings of smaller size at a higher density than the former ink jet recording head 1.
The ink jet recording method is a method of producing images with a recording liquid utilizing a thermal energy in the formation of droplets of the recording liquid.
In the ink jet recording heads with the foregoing structures or ink jet recording heads provided with an orifice plate having discharge openings (orifices) of a predetermined size at the end of liquid path (not shown in the drawings), physical properties of the surface part in the neighborhood of discharge openings, that is, physical properties of tip end parts 5-1 around the discharge opening 5 in FIGS. 1A and 1B or edge parts of supports 10 and 16 and partition wall portion 12, which constitute the discharge openings 14 in FIGS. 1C to 1E, are very important for stable discharge of the ink from the discharge openings.
As a result of many experiments and investigations, the present inventors have found that, when the ink 4 is discharged from the ink jet recording head, the ink 4 attaches to the parts in the neighborhood of discharge opening, and once an ink pool is formed on these parts, the ink scattering direction will be deviated from the normal direction C predetermined direction, and furthermore, the scattering direction will be disturbed at every ink discharge due to the unstableness of the ink pool and no stable ink discharge can be obtained. In other words, no good recording can be obtained. Furthermore, when an ink film is formed entirely on the parts around the discharge opening, random ink scattering, that is, the so called splash phenomenon, appears and thus no stable recording can be obtained, either, or when the ink pool so develops as to cover the,surface including the discharge opening (discharge opening surface), the ink jet recording head will fail to discharge the liquid droplets.
Particularly in the ink jet recording head shown in FIGS. 1C to 1E, a combination of at least two different materials is often used as members that surround the discharge opening 14. For example, three different materials, e.g. silicon for the first support 10, glass for the second support 16 and the cured film of a photosensitive resin for the partition wall portion 12, are used in the ink jet recording head as shown in FIGS. 1C to 1E. Thus, the surface tension differs from one material to another, and a more wettable material is wetted with the ink at first and an ink pool is readily formed on the more wettable material at first, resulting in unstable discharge by liquid droplets. Furthermore, this phenomenon more frequently occurs when the discharge openings are arranged at a higher density to conduct a finer recording or when the discharge is carried out with a high frequency power to attain a high speed recording. Thus, this is an important problem which must be solved to improve the characteristics of an ink jet recording head.
Many attempts have been so far proposed to solve the problem, for example, by treating the ink discharge surface around the discharge opening so as to repel the ink. However, not only mere surface treatment, but also some special treatment is required for the treatment at the ink discharge surface, because the inner surface in the discharge opening, which requires a higher ink liquid wettability, i.e., a high affinity for the ink, is in contact with the ink discharge surface around the discharge opening, which requires a good ink repellency. Thus, it has been so far utilized to fill a removable filler into the liquid path from the discharge opening side and then treat the outside surface around the discharge opening or spray a surface-treating agent onto the ink discharge surface around the discharge opening by a spraying means, while spouting a gas from the discharge opening.
In an ink jet recording head, wherein the partition wall 12 is as thin as, for example 25 .mu.m, and the wall width between the adjacent discharge openings is as small as, for example, 20 .mu.m, to provide discharge openings at a very high density, an ink droplet 4-1 can be discharged straight without wetting the ink discharge surface 14-1 around the ink discharge opening 14, if the ink discharge opening 14 is in the normal state, as shown in FIG. 2A, where the ink is discharged from the discharge opening 14 by subjecting an electro-thermal conversion device 11 to a heat generation, but when a part of the ink discharge surface 14-1 around the discharge opening is wetted with the ink, the ink droplet is discharged in a deviated direction, as shown in FIG. 2B.
The ink discharge surface 14-1 around the discharge opening is wetted with the ink during the ink discharge not only in this manner, but also by an overflow of the ink in a liquid path 13 from the tip end of the liquid path to the outsides, i.e. the surface including the discharge opening, by mechanical vibrations, etc. caused during the mechanical travelling of the ink jet recording head while printing letters or by returning of the ink jet recording head to the original position from the recording paper surface after the contact therewith. Particularly, these phenomena often occur when the discharge openings are formed on the ink discharge surface 14-1 in the neighborhood of the adjacent discharge openings 14, when the discharge openings 14 are formed on the ink discharge surface 14-1 at a high density, and linking of ink wettings takes place to form chains of ink wettings across the adjacent discharge openings and the influence becomes more and more pronounced. As a result, deformation of printed letters or disturbance of printed images takes place to give a considerably adverse effect upon the quality of printed letters or images.
Conventional ink jet recording heads with mirror-finished ink discharge surfaces 14-1 have been studied and it has been found that the mirror-finished ink discharge surfaces are readily wettable with an ink for the foregoing reasons, and thus ink jet recording heads with the mirror-finished ink discharge surfaces further coated with an ink-repellent agent have further been studied. However, it has been found that the foregoing prior art still has the following inherent technical problems with respect to the durability of ink repellency.
That is, conventional ink jet recording heads have been mounted on an ink jet recording apparatus as shown in FIG. 3 to investigate the state in the neighborhood of discharge openings in the ink jet recording heads and the quality of printed images, and have found the following problems:
(1) As one of functions of an ink jet recording apparatus, a mechanism of wiping the ink discharge surface, which has been surface-treated to give an ink repellency, with a rubber blade to prevent the discharge openings from clogging due to the attachment of paper dusts, etc. from recording papers at the initial position of a recording head, etc. Thus, the surface-treating agent layer, that is, the coating layer of a surface-treating agent, is highly liable to peel off when wiped with the rubber blade. PA1 (2) The surface-treating agent layer on the mirror-finished ink discharge surface has a poor durability and often peels off from the boundary surfaces between different materials that constitute the ink discharge surface, when used as a printer for a long time, and the ink repellency is gradually decreased and the quality of printed letters or images is also deteriorated thereby.